This application claims the benefit of the filing date of Taiwan Application Ser. No. 095128067, filed on Aug. 1, 2006, the content of which is incorporated herein by reference.
1. Field of Invention
The invention relates to a voltage regulator for selecting DCDC (Direct Current to Direct Current) and LDO (Low Drop Output), and more particularly to a multi-function voltage regulator capable of selecting the DCDC or LDO without an extra input pad.
2. Related Art
FIG. 1 shows a conventional DCDC voltage regulator 10 in a boost mode. As shown in FIG. 1, the DCDC voltage regulator 10 increases the voltage of a power supply module 11 to a required output voltage Vout. That is, the voltage of the output voltage Vout is higher than the voltage of a voltage source B1. For example, the DCDC voltage regulator 10 increases the voltage of 1.5 volts to the voltage of 3.3 volts. The DCDC voltage regulator 10 includes the power supply module 11, a DCDC control unit 12 and two transistors Q1 and Q2. The power supply module 11 includes the voltage source B1 and an inductor L1 connected in series. The NMOS transistor Q1 has a source connected to a negative terminal of the power supply module 11, and a drain connected to a first node N1, which is connected to a positive terminal of the power supply module 11. The PMOS transistor Q2 has a source connected to the first node N1, and a drain connected to a third node N3 serving as a voltage output terminal. The DCDC control unit 12 further has an input terminal I1 for receiving the voltage of the third node N3. The DCDC control unit 12 outputs a control signal to control actions of the transistors Q1 and Q2 so that the output voltage Vout is held at a predetermined value.
FIG. 2 shows a conventional LDO voltage regulator 20. As shown in FIG. 2, the LDO voltage regulator 20 decreases the voltage of a power supply module 21 to a required output voltage Vout. That is, the voltage of the output voltage Vout is lower than that of the power supply module 21. For example, the LDO voltage regulator 20 decreases the voltage of 3 volts to the voltage of 1.8 volts. The LDO voltage regulator 20 includes the power supply module 21, a LDO control unit 22 and a transistor Q2. The PMOS transistor Q2 has a source connected to a first node N1 and a drain connected to a third node N3 serving as a voltage output terminal. The LDO control unit 22 outputs a control signal to control the action of the transistor Q2 so that the output voltage Vout is held at a predetermined value.
The voltage regulators in FIGS. 1 and 2 respectively utilize the DCDC control unit 12 and the LDO control unit 22, which are different from each other. The architecture and the control method of each of the DCDC control unit 12 and the LDO control unit 22 are well known in the art, so detailed descriptions thereof will be omitted.
In addition, a portable system often has two power systems for respectively providing a higher voltage and a digital core low voltage. The products often use the same integrated circuit and have to use one battery and two batteries, which may be a lithium battery. So, the same power processing system on the system has to transform the powers with different input voltages into an adapted voltage for the system. In order to simplify the circuit in the system, the circuit has to be used repeatedly, and the method for selecting different modes also has to be achieved stably without increasing the cost of the pad.
FIGS. 3 and 4 show voltage regulators having the DCDC and LDO functions, wherein FIG. 3 shows a DCDC voltage regulator 30 and FIG. 4 shows a LDO voltage regulator 40. Referring to FIG. 3, the DCDC voltage regulator 30 similar to FIG. 1 includes a power supply module 11, a voltage control unit 32, and two transistors Q1 and Q2. The voltage control unit 32 and the two transistors Q1 and Q2 are designed in an integrated circuit (IC), as illustrated by the dashed line 35. The voltage control unit 32 also has an additional input terminal I2 for receiving a selection signal, and the selection signal is inputted by the extra pad PA of the integrated circuit 35. In this embodiment, when the selection signal is a ground signal, the voltage regulator is the DCDC voltage regulator. The source of the NMOS transistor Q1 is connected to the negative terminal of the power supply module 11 through the pad of the integrated circuit 35.
Referring to FIG. 4, the LDO voltage regulator 40 similar to FIG. 3 includes a power supply module 21, a voltage control unit 32 and two transistors Q1 and Q2. The LDO voltage regulator 40 and the LDO voltage regulator 30 have almost the same architecture except that the pad PA of the LDO voltage regulator 40 is connected to the positive terminal of the power supply module 21 while the pad PA of the LDO voltage regulator 30 is connected to the negative terminal of the power supply module 21. So, as shown in FIGS. 3 and 4, the DCDC voltage regulator 30 and the LDO voltage regulator 40 use the same voltage control unit 32, and utilize the extra pad PA to serve as input terminal for the selection signal.
As mentioned hereinabove, the voltage regulators in FIGS. 1 and 2 use different control units (i.e., the DCDC control unit 12 and the LDO control unit 22), while the voltage regulators in FIGS. 3 and 4 use the same voltage control unit 32. However, the voltage regulators in FIGS. 3 and 4 need the extra pad PA to serve as the input terminal for different functions of selection signal.